Machines and related processes for forming, filling and sealing flexible, pillow-shaped bags made from continuous packaging film are well known. These machines are widely used to package a variety of loose products, such as snack foods, frozen foods and the like. These machines typically include a continuous web of packaging film, a tube former for converting the web into a hollow tube and a reciprocating carriage with opposed jaws for stripping, sealing and cutting the tube to form a series of filled bags at high speed. One of the most successful approaches for forming bags in this manner calls for the use of a continuous, but variable film feed in conjunction with a constant motion carriage that carries the operating jaws for stripping/sealing/cutting. In particular, this prior art arrangement has a preferred embodiment wherein the carriage is operated at its top speed in order to enable the machine/method to form, fill and seal bags at a rate of up to 120-140 bags per minute. The maximum speed of the carriage determines this high output of the machine and the feeding of the film/tube, the operation of the sealing jaws and other ancillary functions track the carriage motion through a control means, such as a three axis coordinator of a microprocessor. This state of the art machine/method is set forth in an application assigned to the present applicant entitled Continuous Vertical Form-Fill-Seal Packaging Machine With Constant Motion Carriage, Ser. No. 08/12,548, filed Mar. 11, 1994, now U.S. Pat. No. 5,533,222.
While this prior art packaging machine/method out-performs all other continuous machines that we are aware of on a wide variety of loose products, some light weight products, such as potato chips, can occasionally present a problem at the very highest packaging speeds. For example, light weight fragments or crumbs in a product batch of potato chips sometimes have a tendency to float as they fall by gravity along the film/tube. This causes a delay of the entire batch entering the bag before the sealing jaws are closed in order to form the seal and cut the first bag in the series away from the film/tube. When the fragments are caught in the seal area, an imperfect seal can result.
In this prior art machine and method, a partial solution to this problem is offered; i.e. stripping just prior to sealing takes care of removing some of the lagging or late arriving fragments or crumbs from the seal area. The stripper plates are moved downwardly across the seal area relatively faster than the film feed, and in this way the plates are effective to strip any product from the critical zone. While the stripping operation works well, it is for those lightest fragments/crumbs that have the greatest tendency to float where an additional solution is needed. The additional solution should be such as to allow an increase of the output of the package machine or method up to the maximum limit in the range of 120-140 bags per minute. In addition, the solution should not be one that would add additional mass to the carriage, and thus cause a deleterious increase in the operating inertia, thus defeating the purpose of the prior inventive concept. Maintaining maximum carriage speed and thus the least cycle time for the packaging machine/method is a very important aspect of the invention.
It has long been known to employ a clamp for the film/tube above the sealing jaws in order to catch and collect each product batch before it enters the bag being formed. One of the earliest uses of a product clamp is shown in the patent to Tew et al. U.S. Pat. No. 3,256,673. However, as can be seen by viewing this disclosure, a machine or method utilizing the apparatus and techniques taught in this patent provides a maximum cycle time that is more than that demanded in the industry at the present time. The machine in the '673 patent utilizes components that have high inertia and can be operated only in a very slow, intermittent fashion. In addition, the clamp for collecting the product is in a fixed position with no provision for movement, even for adjustment to a different sized bag being formed.
Working from the same basic concept, several attempts have been made to improve the packaging operation using the stationary film/tube clamp concept. Representative arrangements of this type are shown in the Henry et al. U.S. Pat. No. 3,668,815 entitled Vibrating Clamp Product Settler and the Henry U.S. Pat. No. 3,684,254 entitled Vibrating Clamp Product Settler With Interrupter; both the '815 and '254 patents being owned by the present assignee. A similar intermittent operating arrangement utilizing a product clamp, but mounted in a different fashion is illustrated in the McElvy U.S. Pat. No. 4,563,862 entitled Package Forming Apparatus With Combined Holding and Stripper Mechanism, also owned by the present assignee.
While these improved clamp concepts have provided substantial increases in performance, and particularly with regard to vibrating of the clamp to help the settling of the product, neither patent disclosure envisions operating at the maximum speed with continuous film/tube feeding up in the range of 120-140 bags per minute. Other than the vibrating action that promotes the efficient settling of the product, there is no provision for staging of the product batch by moving or extending the clamp along the longitudinal axis of the film/tube for the purpose of both forming and releasing each product batch in the most efficient manner.
At the time of the advances in the vibrating product settler, as shown in the '815 and the '254 patents, and in the similar arrangement for mounting and operating the product clamp as taught in the '862 improvement patent, it was felt by many in the industry that product clamps, with or without vibration, had been utilized to their maximum extent. As far as has been able to be determined, the optimum operating speed and efficiency with the clamps in an intermittent packaging operation had been attained.
However, contrary to the conventional thinking, we have recently discovered that a key additional advance has been overlooked in the area of use of a clamp to enhance the operating efficiency of a machine or method, particularly with continuous film feed. More specifically, the improvement that is now contemplated is in the area of extending or moving the clamp in a longitudinal direction along the film/tube in such a fashion as to be synchronized or coordinated with the sealing jaws on the moving carriage. We have found that it is possible to form the product batch as the clamp is moving, improve the product coalescing and settling within the batch, and then release the batch in the optimum location adjacent the sealing jaws. In this manner, the chance of having lagging crumbs caught in the seal area is virtually eliminated. Furthermore, a significant cycle time reduction and overall speed improvement is attained. Indeed, with the addition of the product clamp with means for extending it along the longitudinal axis of the film/tube, the desired increase in operating speed up into the range of 120-140 bags per minute easily rivals the operation of the more costly machines utilizing the rotating head assembly type machines with multiple carriages.